Metallocene olefin polymerization catalyst systems typically use an activator (also called a co-catalyst) to generate the active catalytic species. In general, there are two catalyst activator families: partially hydrolyzed aluminum alkyl complexes and non-coordinating anions (NCA's). Some of the most commonly employed activators used today are the partially hydrolyzed aluminum alkyls, more specifically, alumoxanes, such as methylalumoxane (MAO). In general, metallocene olefin polymerization systems that utilize NCA-type activators are more active than their MAO counterparts, but are also quite costly and much more sensitive to poisons which present a problem in catalyst synthesis, handling, storage and reactor operation. Alternatively, MAO-based systems are more robust than their NCA-type counterparts, but they suffer from the high cost of MAO production, the fact that MAO is typically used in large excess (relative to the amount of metallocene) and the limited shelf life of MAO.
In order to enhance polymer morphology, metallocene polymerization catalysts operated in industrial slurry and gas phase processes are typically immobilized on a carrier or a support, such as alumina or silica. Metallocenes are supported to enhance the morphology of the forming polymeric particles such that they achieve a shape and density that improves reactor operability and ease of handling. However, the supported versions of metallocene polymerization catalysts tend to have lower activity as compared to their homogeneous counterparts. In general, metallocene and single-site catalysts are immobilized on silica supports.
Alternative supports for metallocene and single-site catalysts have been the subject of numerous ongoing research projects. In particular, metallocenes supported on clay or ion-exchanged layered compounds have generated interest. Olefin polymerization catalysts using clay, clay mineral or acid/salt-treated (or a combination of both) ion-exchange layered compounds, an organoaluminum compound and a metallocene as components have been reported (see EP 0 511 665; EP 0 511 665; and U.S. Pat. No. 5,308,811). Likewise, U.S. Pat. No. 5,928,982 and 5,973,084 report olefin polymerization catalysts containing an acid or salt-treated (or a combination of both) ion exchange layered silicate, containing less than 1% by weight water, an organoaluminum compound and a metallocene. Furthermore, WO 01/42320 discloses combinations of clay or clay derivatives as a catalyst support, an activator comprising any Group 1-12 metal or Group 13 metalloid, other than organoaluminum compound, and a Group 3-13 metal complex. Also, U.S. Pat. No. 6,531,552 and EP 1 160 261 report an olefin polymerization catalyst of an ion-exchange layered compound having particular acid strength and acid site densities. U.S. 2003/0027950 reports an olefin polymerization catalyst utilizing ion-exchange layered silicates with a specific pore size distribution and having a carrier strength within a specific range.
Likewise, alternative activators for metallocenes and other single-site polymerization catalysts have been the subject of numerous research efforts in recent years. For example, perfluorophenyl aluminum and borane complexes containing one anionic nitrogen-containing group may activate metallocenes. For example, R. E. Lapointe, G. R. Roof, K. A. Abboud, J. Klosin, J. Am. Chem. Soc. 2000, 122, 9560-9561, and WO 01/23442 A1 report the synthesis of (C6F5)3Al(imidazole)[Al(C6F5)3][HNR′R″]. In addition, G. Kehr, R. Frohlich, B Wibbeling, G. Erker, Chem. Eur. J., 2000, 6, No. 2, 258-266 report the synthesis of (N-Pyrrolyl)B(C6F5)2. Supported activators containing a Group 13 element and at least one halogenated, nitrogen-containing aromatic group ligand for polymerization catalysts have been reported (U.S. Pat. Nos. 6,147,173 and 6,211,105).
Macromolecules 2002, 35, 6760-6762 discloses propene polymerization with tetrakis(pentafluorophenyl)borate, 7-octenyldiisobutylaluminum, and racMe2Si(2-Me-indenyl)2ZrCl2 or Ph2C(cyclopentadienyl)(fluorenyl)ZrCl2 to produce polypropylene with octenyldiisobutylaluminum incorporated as a comonomer.
Other references of interest include: US 2003/104928; WO 2003/064433; U.S. Pat. No. 6,489,480; U.S. 2002/038036; WO 2002/102811; U.S. Pat. Nos. 6,414,162; 6,040,261; 6,239,062; 6,376,629; 6,451,724; JP 2002-069116A; JP 2002-0253486A; US 2003/0027950; JP 2002-037812A; JP 2002-020415A; JP 2002-060411A; JP 2001-316415A; JP 2001-316414A; U.S. Pat. No. 6,531,552; JP 2001-200010A; JP 2001-163909A; JP 2001163908A; WO 2001/30864; JP 2001-026613A; JP 2001-031720A; JP 2000-198812A; WO 2000/22010; JP 2000072813A; WO 2000/11044; U.S. Pat. Nos. 6,353,063; 6,376,416; JP 11255816A(1999 Sep. 21); JP 11166012A(1999 Jun. 22); JP 11166011A(1999 Jun. 22); U.S. Pat. No. 6,048,817; JP 05025214A(1993 Feb. 02); WO 2003/064433; WO 2003/0644435; JP 2004-83773; U.S. 2007/0185343; U.S. 2005/0267273; U.S. 2005/0245701; U.S. 2013/0289227; U.S. Pat. Nos. 4,874,734; 5,122,491; 5,155,078; 5,234,878; 5,654,248; US 2006/0155083; Polymer 56 (2015) 218-222; JP 2004-83773; and WO 2007/035492.
Given the high cost, low stability and reduced activity of MAO-based metallocene polymerization systems, there is a need in the art for new inexpensive, stable and supportable polymerization catalyst activator compounds.